This invention relates generally to location of a target, and more specifically, to locating target positions utilizing a radar altimeter with terrain feature coordinate location capability.
Target location, in terms of latitude, longitude, and a vertical reference (e.g. elevation), is utilized for all types of targeting processes. Presently utilized target location methodologies include, for example, personnel using visual target location equipment or GPS locators. Using personnel to locate targets with visual locating devices can be dangerous and often times extremely difficult due to terrain ruggedness. Further, the accuracy of the target location is highly dependent on the abilities and skill of the personnel performing the target location. In addition, Global Positioning Satellite (GPS) locating devices are extremely susceptible to jamming.
Radar altimeters are not as easily jammed as GPS devices. One known precision radar altimeter xe2x80x9clooksxe2x80x9d at the ground in a series of narrow doppler swaths, using doppler band pass filters to focus in on one swath at a time. Return signals are received by two or more antennas. The location of the highest point within a particular swath is determined by performing phase comparisons of the return signals received by the two antennas and passed through the particular doppler band pass filter. If the highest point being illuminated by radar is directly below the air vehicle, then the return signal is received by both antennas at the same time. On the other hand, if the highest point is off to one side of the air vehicle, the return signal will be received by one antenna before it is received by the second antenna, because the return path to the second antenna is longer then the return path to the first antenna.
The phase or the time of arrival of the return signals at each of the antennas are compared. The radar altimeter described above can be utilized with digital terrain elevation maps which provide stored latitude, longitude, and elevation data for a given area or terrain.
In one aspect, a method of determining a target location from a vehicle is provided. The method comprises identifying the target utilizing a video system, determining an angular location vector to the target with respect to the vehicle, and determining a position of the vehicle on a digital terrain elevation map with the precision radar altimeter. A location where the angular location vector would intersect with the digital terrain elevation map is calculated and a target position is generated based on vehicle position and the location of the intersection of the angular location vector and digital terrain elevation map.
In another aspect, a target location system for use in a vehicle is provided. The system comprises a telemetry transmitter/receiver communicatively coupled to both a radar altimeter and a video system. The video system identifies targets and provides an angular position of the target to the telemetry transmitter/receiver. The radar altimeter determines a position of the vehicle utilizing digital terrain elevation maps and provides the position of the vehicle to the telemetry transmitter/receiver. The target location system determines a position of the target utilizing the angular location vector, the vehicle position, and a digital terrain elevation map for a vicinity of the target.